The present invention relates to the control of internal combustion engines. More specifically, the present invention relates to a method and apparatus to control a variable displacement internal combustion engine equipped with at least one turbocharger.
Present regulatory conditions in the automotive market have led to an increasing demand to improve fuel economy and reduce emissions in present vehicles. These regulatory conditions must be balanced with the demands of a consumer for high performance and quick response for a vehicle. Variable displacement internal combustion engines (ICEs) provide for improved fuel economy and torque on demand by operating on the principle of cylinder deactivation. During operating conditions that require high output torque, every cylinder of a variable displacement ICE is supplied with fuel and air to provide torque for the ICE. During operating conditions at low speed, low load, and/or other inefficient conditions for a fully displaced ICE, cylinders may be deactivated to improve fuel economy for the variable displacement ICE and vehicle. For example, in the operation of a vehicle equipped with a six cylinder variable displacement ICE, fuel economy will be improved if the ICE is operated with only three cylinders during relatively low torque operating conditions by reducing throttling losses. Throttling losses, also known as pumping losses, are the extra work that an ICE must perform to pump air from the relatively low pressure of an intake manifold, across a throttle body or plate, through the ICE and out to the atmosphere. The cylinders that are deactivated will not allow air flow through their intake and exhaust valves, reducing pumping losses by forcing the ICE to operate at a higher intake manifold pressure. Since the deactivated cylinders do not allow air to flow, additional losses are avoided by operating the deactivated cylinders as xe2x80x9cair springsxe2x80x9d due to the compression and decompression of the air in each deactivated cylinder.
Turbocharging may also improve fuel economy by utilizing wasted energy in engine exhaust gas to increase the performance of an ICE. A turbocharger generally includes a turbine and a compressor. Exhaust gases from an ICE are directed to the turbine housing, causing the turbine to rotate. The turbine concomitantly rotates the compressor to force more air into the engine air intake, increasing the power output of the ICE. The additional pressure generated by the compressor is known as boost pressure, which is typically controlled by a wastegate. The wastegate regulates the flow of exhaust gas over the turbine, controlling the speed of the turbine and the compressor. When high engine power is not needed, the wastegate can bypass the turbine dropping the boost pressure, allowing the engine to run closer to atmospheric intake manifold pressure to minimize the need for throttling and improving fuel economy.
The present invention is a method and apparatus for the control of cylinder deactivation and turbocharging in a variable displacement ICE to improve fuel economy and maintain performance. In the preferred embodiment of the present invention, a six-cylinder internal combustion engine (ICE) may be operated as a three-cylinder engine by deactivating three cylinders. The cylinder deactivation occurs as a function of load or torque demand by the vehicle as determined by variables such as manifold pressure. If the ICE is in a condition where it can deliver the desired torque with partial displacement to improve efficiency, the controller will deactivate the mechanisms operating the valves for the selected cylinders and also shut off fuel and spark to the selected cylinders. The deactivated cylinders will then function as air springs.
Fuel economy for a variable displacement ICE is maximized by operating in a partially-displaced mode or configuration. The present invention maximizes the amount of time spent in a partially-displaced operation while maintaining the same performance and driveability of a fully-displaced ICE. Fuel economy improvement is maximized by entering a partially-displaced configuration as quickly as possible, and staying in the partially-displaced configuration for as long as possible in the operation of a variable displacement ICE.
Turbocharging can further improve the operation of a variable displacement engine operating in a partially-displaced mode by providing a larger torque range within which the engine can operate in the partially-displaced mode and/or by further reducing throttling losses if the engine displacement is reduced from its original size. A turbocharger can assist in engine transient operation by its ability to regulate air flow. For example, when the engine switches from partially-displaced to fully-displaced mode, the turbocharger can provide immediate increase in air flow without throttle movement.